To Tell the Truth...Are Parkinson's Patients Capable of Lying?

Up until a few years ago, it was believed that those with Parkinson's disease, were only severely limited in their physical capabilities. Parkinson’s is a neurodegenerative disease that is characterized by the progressive destruction of the brain cells located in the person’s substantia nigra. These cells are responsible for the production of dopamine, a neurotransmitter that facilitates the synapses between the neurons in this area.

The destruction of these cells—and their subsequent replacement by Lewy Bodies—causes several symptoms in the affected individual, such as bradykinesia, muscle rigidity, and tremors. However, on top of these physical symptoms that slowly progress as the disease runs its course, Parkinson’s disease is also reported to modify the patient’s behavioral traits, resulting in different personality traits in the person than when before they developed the disease. These changes affect, among other things, the patient’s commitment to certain tasks, as well as their honesty, specifically with the fact that Parkinson’s patients tend to be extremely inflexible and cannot easily tell lies like others.

Parkinson’s is among one of the most common neurodegenerative diseases, standing in second place behind Alzheimer’s. It is spread across the globe and affects both male and female individuals equally. The disease, however, is more common in those over 60 years of age, though there exists an early-onset variant that, while uncommon, may affect those aged 40 and under.

Due to its neurodegenerative nature, those affected with Parkinson’s will slowly degenerate over time; slow at first, but increasing in aggressiveness as the disease evolves. Regrettably, despite our current understanding of the disease, and the mechanisms behind the symptoms it generates in the patient, we still don’t exactly know the actual element that triggers Parkinson’s in the first place.

There are several theories regarding the onset of Parkinson’s, with the most accepted one stating that the disease, though unknown in exactly what triggers its origins, is supposedly caused by a combination of environmental and genetic factors, coupled with oxidative damage, alongside the natural aging process. It is believed that the cerebral-intestinal connection also plays an important role in the development of Parkinson’s; there have been several studies that link an underlying and undiagnosed celiac disease with the onset of Parkinson’s. In the same vein, following a gluten-free diet has also been observed to create improvements.

Those who are afflicted with Parkinson’s have been reported to age ‘differently’, in the sense that the disease may alter the brain’s chemistry, resulting in a wide variety of personality traits in those who suffer from it. Specifically, and as was mentioned above, Parkinson’s patients tend to be overly inflexible when it comes to most things, including adopting new tasks or even telling lies.

Parkinson's disease effect on lying in patients

A study featured in the journal Brain, performed by Abe et al, researched the effect of Parkinson’s on the subject’s personality. The research team pointed out that, just like the rigidity and motor difficulties in the patient’s muscles, they also had a similar mental rigidity, which results in behavioral differences in relation to healthy individuals. The study in question discovered that Parkinson’s patients told fewer lies during tasks where they were told to do so. Furthermore, the study also found that the metabolic rate in the areas of the brain linked with deceptive behaviors was lower in healthy individuals.

In this sense, when it comes to deceptive behaviors and lying, in general, it’s not that Parkinson’s patients can’t do it, it’s just that they have a much harder time doing so compared to healthy individuals. Determining whether these traits surfaced due to the disease, as opposed to behavioral changes brought about by the natural aging process, was a particularly challenging task.

The study in question addressed this concern by citing another researcher’s findings, which stated that, although the possibility of Parkinson’s targeting mostly ‘honest’ individuals cannot be ruled out, it was discovered that these behavioral changes happened as a neuropathological symptom in the course of the illness. In this sense, those who suffer from Parkinson’s disease become more honest not due to the natural aging process, but due to Parkinson’s specific brain damage, which manifests in honest behaviors with increasing frequency. This isn't because they choose to be honest, but it's because they have a harder time telling lies or acting dishonest, in general.

Upon closer examination, researchers found that a possible cause for these honest behaviors may come from damage to the prefrontal cortex, which is a structure that plays a vital role in complex cognitive processes, such as deception, as well as supporting the use of executive functions. It has been assumed by several researchers that the prefrontal cortex, specifically the lateral prefrontal cortex, supports complex cognitive processes and executive functions such as response inhibition and cognitive control. Consequently, damage to this area is linked to executive dysfunction in affected individuals, which results in difficulties with certain actions, such as functional flexibility, and showing goal-directed behaviors, both of which are crucial elements in deceptive behaviors.

To prove this, the study took 32 idiopathic Parkinson’s patients, alongside 20 age-and-sex-matched controls. These individuals were first tested to determine if they had a deficit in their memory. They achieved this by showing them pictures of objects to confirm if both groups remembered what these objects were. Furthermore, to further confirm an absence of memory deficit, the subjects were also tasked with telling if the objects were animate, or inanimate.

After this initial screening process, the participants were subjected to an experimental deception task, which presented them with videos of 4 actors holding up a picture and asking “Have you seen this?”. The subjects were asked to respond truthfully to 3 of these questions and asked to lie to one of the actors, in order to measure the patient's’ ability to lie. The results, as expected, showed a small, yet notable difference between both groups: while the controls had next to no difficulties when following instructions, the Parkinson’s patients had considerable difficulties when asked to lie. The schism between these groups was small (less than 10% of difference); however, considering the simplicity of the task, and that both groups correctly passed the screening process, it is safe to assume that, due to their disease, Parkinson’s patients have a biological component which makes it harder for them to tell lies or act deceptively.

In conclusion, and contrary to popular belief, Parkinson’s does not to target mostly honest individuals. On the contrary, these honest behaviors result due to damage to the brain’s lateral prefrontal cortex, which negatively impacts executive function, including crucial traits to human deceptive behavior.

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